That's simply untrue. Look at any serious programming books. And LaTeX is used as the back-end for quite a number of text-processing tools.
Professional publishing has long ago switched to DTP tooling, able to handle layouts and colouring in modern presses.
To be fair, the use cases are rather different. Regular fiction books are not so complicated in terms of layout. Magazines are generally involve much more complicated layouts - where there are questions of getting colours right, having text wrap, and so on.
But for technical work, it's insane to use anything not TeX-based (e.g. Scribble), even if you don't use TeX directly.